In the medical balloon art, medical balloons have been reinforced by placing fibers into pre-determined arrangements using manual or partially automated processes, as described in U.S. Pat. No. 6,746,425, which is incorporated by reference in its entirety. Some manual and partially automated manufacturing processes require the manual manipulation of fibers to properly dispose the fibers in the desired location of the balloon. The non-automated aspects of such processes increase the cost and time investment to manufacture a reinforced medical balloon as compared to highly automated processes. Also, the non-automated aspects of such processes, and the time associated with manual processes, prevent or impede the formation or efficient disposition of complex fiber patterns, or the formation of complex weave patterns that facilitate the disposition of a two-dimensional fabric over a three-dimensional contour associated with a medical balloon. It is also believed that automated processes facilitate a more precise and consistent disposition of fibers that is either impossible or difficult to achieve with manual or partially automated processes.
Braiding technologies and 2D and 3D braiding machines are described in: “Braiding,” 2005 Advanced Composite Materials & Textile Research Laboratory, University of Massachusetts-Lowell, available at the University of Massachusetts-Lowell's Advanced Composite Materials & Textile Research website. Braiding technologies and Cartesian braiding machines are described at the website of 3TEX, Inc. A report by the National Textile Center (NTC) of Springhouse, Pa., describes braiding patterns and describes the behavior of braids under tensile load, and the effect of yarn angle with respect to load and jamming condition, in “Engineered Non-Linear Elastic Blended Fabrics,” NTC Project F00-PH05 2005. The following articles describe braids: Guang-Wu Du, Tsu-Wei Chou, and P. Popper, “Analysis of three-dimensional textile pre-forms for multidirectional reinforcement of composites,” J. Mater. Sci. 26 (1991) 3438-3448; M. Dunn, E. Armstrong-Carroll, Y. Gowayed; “Engineered Non-linear Elastic Bland Fabrics”; W. Seneviratne, J. Tomblin, “Design Of A Braided Composite Structure With A Tapered Cross-Section,” National Institute for Aviation Research Wichita State University Wichita, Kans. 67260-0093; and The Department Of Defense Handbook Composite Materials Handbook Volume 2, “Polymer Matrix Composites Materials Properties,”. Braiding technology is also described in U.S. Pat. Nos. 5,718,159, 5,758,562, 6,019,786, 5,957,974, 4,881,444, 4,885,973, and 4,621,560. Each of the above-identified references are incorporated by reference herein.
For medical balloons, very thin walls are desirable. To reduce wall thickness, it is necessary to reduce the thickness of each fiber and increase the number of fibers to supplement for the reduced strength of the thinner fibers. If the thickness of the fibers is reduced, it is necessary to increase the number of fibers, and the fiber density, by the square of the reduction in thickness, in order to maintain the same tensile strength in the reinforced balloon wall. It is believed that the reduction of fiber thickness leads to a problem when the fibers are braided. This is because of the bunching or jamming effect that occurs when a continuous braided fabric is disposed over a cylindrical portion of a balloon and then continued over a portion of the balloon with a reduced diameter, such as when a fabric extends from a cylindrical balloon form to a conical end of the balloon. It is also believed that the same problem exists when a fabric is disposed over any three-dimensional object that reduces from one diameter to a smaller diameter.
At the conical end of a balloon, the fiber density increases as the diameter of the balloon decreases, as the same number of fibers are made to cover a decreasing circumferential area. If the weave pattern is changed to allow for a lower fiber density at the areas of reduced diameter, the wall thickness can become too thin and a transition to a different fiber angles in the weave can cause the fibers to bunch or jam and prevent further reduction in balloon diameter. Also, sparse braiding provides for greater spacing between fibers and thereby increase the jamming angle between fibers, and wall thickness is sacrificed in the main part of the balloon because of the inverse square relationship between the wall thickness and the fiber density required to achieve a constant wall strength. In other words, the fibers need to get thicker to maintain the reinforced strength per unit area of the balloon wall. As a result, the fiber density limitation at the balloon ends dictates a sub-optimal fiber density—and concomitant wall-thickness—over the central region of the balloon where the diameter is largest.